MAINTAINERS: Adjust ARM/NOMADIK/Ux500 ARCHITECTURES to file renaming

Commit 8f00b3c41ae7 ("mfd: db8500-prcmu: Rename register header") renames
dbx500-prcmu-regs.h to db8500-prcmu-regs.h in drivers/mfd/ but misses
to adjust the ARM/NOMADIK/Ux500 ARCHITECTURES section in MAINTAINERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

warning: no file matches F: drivers/mfd/dbx500*

Remove the obsolete file entry after this file renaming.

Signed-off-by: Lukas Bulwahn <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

MAINTAINERS

···
 F:	drivers/mfd/ab8500*
 F:	drivers/mfd/abx500*
 F:	drivers/mfd/db8500*
-F:	drivers/mfd/dbx500*
 F:	drivers/pinctrl/nomadik/
 F:	drivers/rtc/rtc-ab8500.c
 F:	drivers/rtc/rtc-pl031.c